1. Technical Field
The present technology relates to a run flat tire, and particularly relates to a run flat tire configured so as to have both durability when run-flat traveling and riding comfort when regular traveling.
2. Related Art
In run flat tires provided with a side reinforcing layer having a falcated cross-section on an inner surface side of a side wall portion, methods such as increasing a thickness of the side reinforcing layer and using a rubber with a high hardness have been used in order to ensure durability when run-flat traveling. However, when only these sorts of technologies are applied there are problems in that the degree of excellent run flat durability that can be ensured is limited and riding comfort when regular traveling is significantly worsened due to the increase in side wall stiffness.
Particularly, when the tire cross-sectional height reaches a certain height, tire breakdowns when run-flat traveling consist mainly of breakdowns in the vicinity of the rim cushion near the bead portion. Therefore, there is a demand for technology that prevents such tire breakdowns and, simultaneously, ensures riding comfort.
Technology has been proposed to solve this problem wherein a mitigating rubber layer is disposed in the vicinity of a rim line on an outer side, in a tire axial direction, of a folded up portion a carcass layer, wherein, when a side wall portion buckles, the mitigating rubber layer exerts a mitigating action with respect to the upthrust by a rim flange between the carcass folded up portion and the rim flange in order to prevent rupturing in that area (e.g. see Japanese Unexamined Patent Application Publication No. H07-304312A). Additionally, technology has been proposed wherein a folded up end of a carcass layer is distanced from a region which contacts a rim flange top edge in order to suppress the generation and/or expansion of cracking due to the concentration of stress in the vicinity of the folded up end of the carcass layer (e.g. see Japanese Unexamined Patent Application Publication No. 2009-61866A).
However, both of these proposals are limited as to effectiveness in enhancing run-flat durability, and, at the same time, do not directly lead to improvements in the effectiveness of enhancing riding comfort when regular traveling. Therefore, neither provides technology that can sufficiently satisfy the demand for both run-flat durability and riding comfort.